Analog-to-digital encoder



Nov. 10, 1970 I E. PACKARD 3,540,036

I ANALOG-TO-DIGITAL ENCQDER Original Filed- Feb. 1. 1965 s Sheets-Sheet 1 FIG. 2 4

EDWARD L. P CKARD BY M0471 ATTORNEY INVENTOR.

Nov. 10, 1970 E. PACKARD ANALOG-TODIGITAL ENCODER 6 Sheets-Sheet 3 Original Filed Feb. 1, 1965 Nbv. 10, 1970 E. PACKARD 3,540,036

ANALOG-TO-DIGITAL ENCODER Original Filed Feb. 1. 1965 6 Sheets-Sheet 4 Nov. 10, 1970 E. L. PACKARD 3,540,035

ANALOG-TO'DIGITAL ENCODER Original F-iled Feb. 1. 1965 6 Sheets-Sheet 5 United States Patent 3,540,036 ANALOG-TO-DIGITAL ENCODER Edward L. Packard, Glendale, Califi, assignor t0 Singer- General Precision, Inc., a corporation of Delaware Continuation of application Ser. No. 429,350, Feb. 1, 1965. This application July 22, 1968, Ser. No. 757,171 Int. Cl. G08c 9/04 US. Cl. 340-347 2 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a novel and improved magnetic analog-to-digital encoder having a ferrite disc with milled raised and recessed segments, a shunt plate associated with the pickup cores and a ferromagnetic backp-late. The entire disc is magnetized with the N-S poles on the top and bottom surfaces of the disc. Toroidal coils, equivalent to contact brushes of a conventional brush contact analogto-digital converter or encoder are supported in space related position adjacent the raised and recessed segments. A suitable AC generator supplies electrical power to the toroids driving them near but not at saturation. As the raised segments of the disc pass under the toroids, the magnetic flux from the raised segments, having -a shorter air path greater than it is when a recessed segment is under the toroid. Consequently the magnetic influence of the flux flowing from the N-pole surface of the disc to the S-pole-surface of the disc has a greater influence on the toroids when over a raised segment than when over a recessed segment.

In order to provide magnetic return path through the coils, they are backplated and supported by a ferromagnetic plate. In order to prevent magnetic leakage and cross talk to a recessed portion from an adjacent raised portion a shunt plate is provided. Said shunt plate having holes therein receives therethrough the ends of the cores of the toroids and is positioned between the disc and the wind ings on the toroids. A single insulating disc having'holes therein also accepts the ends of the cores therethrough and is positioned between the shunt plate and the windings and protects the windings from shorting out on the shunt plate. This protection greatly simplifies the construction of these encoders and greatly enhances the ruggedness of the encoder.

This application is a continuation of application Ser. No. 429,350, filed Feb. 1, 1965, now abandoned.

This invention relates to encoders and more particularly to a novel and improved magnetic encoder provided with means to protect the pickup heads from stray magnetic flux influence.

Magnetic encoders of the prior art give poor resolution of the signal produced therefrom in the area of the disc producing a low magnetic inductance which usually in dicates a binary l and are diflicult to distinguish from a high inductance area which produces a binary 0. This poor resolution is caused by the stray lines of magnetic flux entering readout elements when the elements are over areas of low magnetic inductance and, in fact, are supposed to be detecting little or no magnetic inductance or lines of flux. In the prior art the only way known to overcome this problem was to make the pickup head-to-disc spacing as close as possible. This method was only partially effective.

Maintaining the close pickup head-to-disc spacing brought about the advent of new problems. One such problem was, due to the use of these close tolerances, shock and vibrations of the encoder causing collisions between the heads and disc during the encoder operation thereby causing damage resulting in repair costs or replace- Too ment of the encoder. In either case, an expense is incurred and the reliability of the encoder is reduced.

An added disadvantage of the normally required readout element-to-information member spacing is that during assembly the maintaining of these tolerances increases the manhours spent in adjustment thereby increasing the overall manufacturing costs.

The present invention provides an analog-to-digital encoder of the magnetic non-contact type which exhibits a high zero-to-one ratio of the readout signal and does not require the close pickup head-to-information member spacing to attain the high resolution, and yet is not affected by stray magnetic flux lines.

Briefly described, this invention provides an analog-todigital encoder comprising a coded information member having a plurality of tracks of different ordinal significance. Each track is divided into a plurality of segments, each exhibiting one of two different magnetic flux densities. Readout means are associated with each track to detect the intensity of the magnetic flux and a shunt plate is associated with said readout means to shunt back to the opposite side of the disc substantially all of the magnetic flux not intended for a particular pickup head. Noise and crosstalk is thereby reduced to a minimum.

In the drawings:

FIG. 1 is a section view of an analog-to-digital encoder embodying this invention;

FIG. 2 is a view of one of a plurality of pickup elements of the analog-to-digital encoder embodying this invention;

FIG. 3 is an enlarged partial sectional view of the lefthand side of the encoder embodying this invention and illustrating the flow of magnetic flux when a pickup head is over a raised segment of the second least significant digit track and the air gap between the pickup and the disc is at a minimum;

FIG. 4 is an enlarged partial sectional view of the encoder shown in FIG. 3 but with the pickup head over a recessed segment and distance of the air gap between pickup and disc is at its greatest;

FIG. 5 is a top plan view of the encoder disc shown in FIG. 1 illustrating the encoder pattern of a seven bit V scan encoder taken along the line 5-5 of FIG. 1.

FIG. 6 shows an enlarged view taken along the lines 66 of FIG. 1 and shows a backplate into which the pickup elements are mounted and which also serve as a return path for the magnetic lines of flux emanating from the information member of FIG. 2;

FIG. 7 shows an enlarged view taken along the lines 77 of FIG. 1 and shows a shunt plate which serves as an alternate flux path for the lines of flux not intended for a readout element; and

FIG. 8 is a schematic block diagram of typical V-scan readout circuitry employing this invention.

Referring now to the drawings, wherein there is shown a preferred embodiment of this invention and wherein like reference numerals indicate like or corresponding parts throughout the several views. The numeral 10 indicates a rotating shaft preferably of a ferromagnetic type stainless steel having both a low magnetic reluctance and low retentivity. Shaft 10 receives analog quantities in the form of angular positions and is mounted in a housing 12 preferably formed of aluminum, or the like, which may be in two sections for accessibility. The two sections are held together by bolts 14. Bearings 16 may be used to allow friction-free rotation of shaft 10 within the housing 12.

Mounted on shaft 10 within housing 12 is an information disc 18 comprising an aluminum backing 20 with a sleeve 22 provided thereon, as shown. Backing 20 is firmly afiixed to shaft 10 to rotate therewith. Firmly mounted upon (as by cementing or the like) aluminum backing 20 is a magnetized information code disc 24, a plan view of which is seen in FIG. 5. Disc 24 is composed of a highly magnetized barium ferrite. This particular code disc 24 in this embodiment is composed of INDOX I, a trademark of Indiana General Corporation. But it is to be understood that other suitable magnetized discs may be used.

As best illustrated in FIGS. 1 and 5, code disc 24 comprises a plurality of concentric tracks having raised and recessed segments, designated by the numerals 32 and 34 respectively.

conventionally, each track, beginning with the outside as the least significant digit and progressing inwardly, signifies a more significant digit. All raised segments in every track exhibit the same magnetic characteristics and all recessed segments in every track exhibit the same magnetic characteristics. This encoder employs a standard V scan antiambiguity pattern which in this embodiment the tracks are skewed for better readout element spacing. Of course, it must be understood that other disc patterns may be employed and that this pattern was chosen only as a preferred embodiment.

A backplate 36 is mounted in the top section of housing 12 by bolts 58, as shown in FIGS. 1, 3 and 4. Backplate 36 is preferably composed of a suitable ferromagnetic material such as Armco, trademark of the Armco Steel Corporation. Other suitable ferromagnetic material can be employed as long as it has both a low magnetic retentivity as well as low magnetic reluctance.

A plurality of readout or pickup elements 40 sense changes in the magnetic flux density caused by the position changes of the segments 32 and 34.

Each pickup 40 consists of a toroid core 41 as shown in FIG. 2, which in this embodiment is toroidal in shape. A winding 42 is series wound around each leg of core 41. Preferably, core 41 is composed of a saturable magnetic material exhibiting two remanent states.

Particular positioning of pickups 40 is also in standard V-scan arrangement as shown in FIG. 6. Least significant digit track 30 has a pickup element 40 placed in slot 44. Cores 41 of pickup 40 are cemented into the slots 44 in backplate 36. A pair of holes 46 through plate 36 is provided on either side of slot 44 and each is provided with an insulated sleeve 48. Leads 50 of winding 42 (FIGS. 2 and 6) extend through holes 46 and are connected to a circuit board 52 and subsequently to a V-scan selection circuitry; (schematically illustrated in FIG. 8) the functions of which will be explained later.

A shunt plate 54, as best shown in FIGS. 3 and 7, is clamped to'a ring 56 by bolts 58. Shunt plate 54 and ring 56 are composed of a ferromagnetic material the same as backplate 36 and they may be constructed in one piece or made separate. A space 61, best shown in FIGS. 3 and 4, is provided between sleeve 22 and shunt plate 54 for clearance, thus when the shaft rotates there will be no friction between the two.

A plurality of slots 62 are provided in shunt plate 54, as shown, which are adapted to receive therethrough cores 41 of the ends of the cores of pickup 40. In this preferred embodiment the cores extend through the shunt plate and the bottom of each core 41 is flush or coplanar with the bottom of shunt plate 54.

OPERATION Before turning to the readout circuitry shown in FIG. 8, an explaantion of the operation of this encoder will now be presented.

Referring to FIG. 3, core 41 is shown over a raised segment 32 which exhibits a high degree of magnetic influence on the core. The magnetic lines of flux creating this influence are depicted in this view by the broken lines 64. In this particular embodiment the surface of code disc 24 closest to core 41 is illustrated as the north pole and the surface near backplate 20 is considered the south pole; therefore. when a readout element 40 has its core 41 adjacent raised portion 32, the air gap between disc 24 and core 41 will be shortest and the lines of flux 64 will become concentrated through the core 41 as they take the path of least magnetic reluctance. In this particular case with core 41 positioned over raised portion 32, more lines of flux 64 flowing through core 41 will cause a drop in impedance in the windings. Magnetic lines of flux 64 will, at this position, flow through backplate 36, shaft 10 and back into the south pole of the magnetized code disc 24 through backing 20. This will then complete the closed magnetic flux circuit.

Turning now to FIG. 4, a different condition is now present. Core 41 of readout element is adjacent a recessed segment 34 and because of the increased distance between the core 42 and the bottom surface of recessed segment 34, magnetic lines of flux 64 will take only the path of least resistance which is now through shunt plate 54. The magnetic influence on core 41 will have now dropped to a minimum. Lines of flux 64 concentrating into shunt plate 54 will then flow through shunt plate 54 to shaft 10 and back into the south pole of the magnetic code disc 24. Therefore, because of the shunting action of shunt plate 54, virtually no magnetic lines of fiux 64 will enter core 41 which, accordingly, moves to a lower remanent state. Winding 42 therefore has an increase in impedance. Less current flows to ground and more current fiows into diodes 61 thus triggering flip-flop readout circuitry, as will be explained later.

It must be understood that the particular polarization of the magnetic code disc 24 is shown by way of example and the opposite could be employed.

Referring now to FIG. 8, there is shown typical readout circuitry as associated with this encoder wherein a kilocycle generator 65 provides an alternating signal to each readout element 40a to 40g.

If the cores of elements 40a to 40g are conducting a high flux density or are saturated by magnetic lines of flux 64, the inductance in windings 42 will drop. If little or no flux 64 is passing through the cores, the impedance in the windings will remain high and the signal from generator .65 will not be grounded.

A resistor 66 is provided to each readout element 40a to 40g, lead and lag, to provide a current thereto and may have, for example, a resistance of 680 ohms. Coupled to each of the resistors 66 and readout elements 40 is a diode 61 provided to rectify the signals to subsequent circuitry. Readout element 40a is associated with the least significant digit track of code disc 24. The least significant digit signal is applied to AND gate 68 and also to AND gate 70 but through an inverter 72. The signal from the next least significant digit track detects the remanent state of leading readout element 40b and lagging readout element 40b. Readout element 40b is coupled into AND gate 68 and, if both of these signals are high, that is, both over a segment of low flux density or a recessed segment 34, AND gate 68 is enabled allowing a signal to be applied to OR gate 74 and subsequently OR gate 74 will produce a binary signal 2 If, on the other hand, the signal from readout element 40a is low, that is, adjacent a segment of high flux density (a raised segment), a high signal will be applied to AND gate 70, and if a high signal is also applied to this same AND gate 70 from lagging readout element 40b, AND gate 70 will be enabled thereby enabling OR gate 74 to produce a binary signal 2 Therefore, it can be seen that if the readout element produces a high signal because it is over a segment of low flux density, the lead readout element 40b will be interrogated, but if the readout element 40a is over a segment of high flux density, the readout element 401) will produce no signal when interrogated and an inverted signal therefrom will allow lagging readout 40b to be interrogated.

This same principle is likewise applied to all succeeding digits of progressing value and this can be better understood in light of the teaching in Patent No. 3,056,956

of an analog-to-digital encoder granted to L. P. Retzinger on Oct. 2, 1962.

Various modifications are contemplated and may ob- Having thus described the invention, what is claimed 1. An analog-to-digital encoder comprising:

(A) a magnetized information disc having a plurality of concentric tracks of different ordinal significance, each of said tracks having alternate raised and recessed segments and said disc being permanently magnetized with the lines of flux extending normal to the surfaces of said disc whereby the raised segments exhibit a greater magnetic influence at the surface of the disc than the recessed segments;

(B) at least one pickup head for each of said tracks, each of said pickup heads comprising a saturable toroidal core having two remanent states and a winding thereon, each of said cores being positioned adjacent the surfaces of said disc whereby one particular remanent state is created within the core when said core is positioned adjacent a raised segment of said disc and a different remanent state is created within said core when said core is positioned adjacent a recessed segment of said disc;

(C) a ferromagnetic backplate mounting said pickup heads thereon and providing a flux return path to said disc, and

(D) a ferromagnetic shunt plate having a plurality of openings therein receiving the ends of said cores therethrough and positioned between said information disc and the windings on said pickup heads.

2. An analog-to-digital encoder comprising:

(A) a magnetized information disc having a plurality of concentric tracks of different ordinal significance, each of said tracks having alternate raised and recessed segments, said disc being permanently magnetized with the lines of flux extending normal to the surfaces of said disc whereby the raised segments exhibit a greater magnetic influence at the surface of said disc than the recessed segments;

(B) at least one pickup head for each of said tracks, each of said heads comprising a saturable toroidal core having two remanent states and a winding thereon, each of said cores being positioned adjacent the surface of said disc whereby one particular remanent state is created within the core when said core is positioned adjacent a raised segment of said disc and a different remanent state is created within said core when positioned adjacent a recessed segment of said disc;

(C) an electrical generator supplying a potential to the windings of said cores;

(D) means for detecting changes in the inductance in said windings when different remanent states are created within said core;

(E) a ferromagnetic backplate mounting said pickup heads thereon and providing a flux return path to said disc; and

(F) a ferromagnetic shunt plate having openings therein receiving the ends of said cores therethrough and positioned between said information disc and the windings on said pickup heads.

References Cited UNITED STATES PATENTS 3,182,305 5/1965 Wolff 340-347 3,251,054 5/1966 Simon 340347 3,281,825 10/1966 Corl et a1. 340347 3,281,826 10/1966 Mofiitt 340-347 MAYNARD R. WILBUR, Primary Examiner C. D. MILLER, Assistant Examiner 

